Certain diesters of 2-mercaptobenzazoles



3,256,294 CERTAIN DIESTERS F Z-MERCAPTO- BENZAZOLES John J. DAmico, Dunbar, W. Va., assignor to Monsanto Company, St. Louis, Mo., a corporation of Delaware No Drawing. Filed Oct. 16, 1964, Ser. No. 404,500

4 Claims. (Cl. 260307) where Z is O or NH. More particularly, the invention relates to S, S'-bis(2 benzimidazolyl)-1,2-dithiooxalate, S, S-bis(2-benzoxaxolyl)-1,2-dithiooxalate, carbonyl bis- 3-(2-benzothiazolineth ione) and 2,2'-(benzoxazolyl) dithiocarbonate. It also relates to a new method for preparing 2,2'-thiobis(benzothiazoles).

An object of the invention is to provide new and useful compounds by reacting heterocyclic mercaptans with oxalyl chloride.

A further object of the invention is to provide animproved composition with herbicidal properties against various grasses and broadleaf plants.

A further object of the invention is to provide an improved composition having antidegradant properties in natural rubber.

A further object of the invention is to provide improved compositions which accelerate the vulcanization of rubber.

A further object of the invention is to provide improved compositions which are useful as fungicides.

A further object of the invention is to provide a new method for the synthesis of 2,2-thiobis(benzothiazoles).

The S,S'-bis(Z-benzimidazolyl)-l,2-dithiooxalate was prepared in the following manner. To a stirred slurry containing 90.2 grams (0.6 mole), of Z-mercaptobenzimidazole and 600 ml. of anhydrous benzene, 42 grams (0.33 mole) of oxalyl chloride was added dropwise at 50 to 60 C. over a 15-minute period. The stirred reaction mixture was heated at reflux for 5 hours. After cooling to 5 C., the solid product was collected by filtration and air dried at 25 to 30 C. The product, S,S'-bis(2-benzimidazolyl)-1,2-dithiooxalate, melting point 195 -197 C. with decomposition, was obtained in 99% yield. The elemental analysis, molecular weight, ultraviolet and in- A United States Patent 0 "ice tillation of the residue in vacuo furnished diethyl oxalate, boiling point 96-97 C./20 mm, in 75.2% yield. The infrared spectra of the diethyl oxalate derived from this method and an authentic sample were superimposable. These data further support the structure assigned to the product.

S,S'-bis(2-benzimidazolyl)-l,2-dithiooxalate has contact herbicidal properties. The test for contact herbicidal properties consisted of several steps. First, a counted number of seeds of various grasses and broadleaf plants (listed in Table I, infra) were planted in standard soil in a flat aluminum pan. The pan used had been perforated on the bottom for proper drainage. The pans of planted seeds were placed in a moist greenhouse bench and allowed to take up water from below as needed. Two weeks after the resulting seedlings emerged they were sprayed with 6 cubic centimeters of a 0.5% concentration spray of S,S' bis (2-benzimidazolyl)-1,2 dithiooxalate. The amount of spray applied to the test area was equivalent to approximately 9 pounds per acre. After 14 days, the plants were observed and all injuries were noted. The degrees of injury are given in Table I under herbicidal rating.

In Table I, 2 indicates moderate injury and 4 indicates that the plants were dead at the time of observation.

S,S'-bis(2-benzimidazolyl)-1,2 dithiooxalate also displayed antidegradant properties in natural rubber. It doubled the tensile strength of natural rubber as compared to an untreated control after aging 7 hours at 121 C. under 80 pounds air pressure per square inch. The protected rubber contained 1.5% by weight of the aforesaid antidegradant.

The S,S-bis(2-benzoxazolyl)-l,2-dithiooxalate and 2,2-

,(benzoxazolyl)dithiocarbonate were prepared in the following manner. To a stirred slurry containing 60.4

. grams (0.4 mole) of 2-mercaptobenzoxazole and 600 ml.

chloride was added dropwise at to C. over a 15- minute period. The stirred reaction mixture was heated frared spectra were in agreement for the compound S,S'--

are 16.27% nitrogen and 18.62% sulfur.

The product, S,S'-bis(2-benzi-midazolyl)-1,2-dithi0oxalate, reacted rapidly with ethyl alcohol. For example, a stirred slurry containing 68.9 grams (0.2 mole) of the product described in the preparation, supra, and 100 ml. of ethyl alcohol was heated at reflux for 4 hours. After cooling to 0 C., the solid was collected by filtration and air dried at 25 to 30 C. The 2-mercaptobenzimidazole, melting point 302-303 C., was obtained in 97% yield. After recrystallization from ethyl alcohol the melting point remained unchanged. A mixture melting point with an authentic sample was not depressed and the infrared spectra of the two were superimposable. The filtrate was distilled at 760 mm. to remove excess alcohol. The disat reflux for 24 hours. After cooling the stirred reaction mixture to 30 C., the precipitate was collected by filtration and air dried at 25 -30 C. The product, MP.

176 C. with decomposition, was obtained in 41.2%

yield. After recrystallization from ethyl acetate-acetone, it melted at 176l78 C. with decomposition. The elemental analysis, molecular weight, ultraviolet and infrared spectra were in agreement for the compound 2,2- (benzoxazolyl)dithiocarbonate. This product was found to be a useful fungicide for the control of rhizoctonia and pythiurn.

. Another product was isolated from the filtrate. The benzene and'oxalyl chloride were removed from the filtered solution in vacuo at a maximum temperature of 30 C. at 1 to 2 mm. pressure. The resulting solid was air dried at 25 to 30 C. The product, melting point 131133 C. with decomposition, was obtained in 57.7% yield. After recrystallization from ethyl acetate, the product melted at 154155 C. with decomposition. The elemental analysis, molecular weight, ultraviolet and infrared spectra were in agreement for the compound S,Sbis(2-benzoxazolyl)-1,2-dithiooxalate. Nitrogen and sulfur analysis of this product showed 7.92% nitrogen and Patented June 14, 1966 18.01% sulfur. Calculated percentages for C H N O S are 7.86% nitrogen and 18.00% sulfur. S,S-bis(2-benzoxazolyl)-l,2-dithiooxlate was found to mildly accelerate the vulcanization of rubber. It was also found to be a formation of '2,2-(benzothiazolyl)dithiocarbonate from a reaction of sodium-2-mercaptobenzothiazole and carbonyl chloride, as a pale yellow solid, soluble in benzene which melted at 134 C. Investigation of this reaction vibration.

1,332 strong 728 medium O=S stretching.

CN stretching.

C--H out-of-plane deformation of 1,2-substituted phenyl group.

fungicide useful for the control of rhizoctonia and 5 confirmed that the product melted at about 134 C., but pythium. analysis thereof revealed that it was a mixture of 2-mer- An attempt was made to prepare the corresponding dicaptobenzothiazole and 2,2-thiobis(benzothiazole) incarbonyl compound from mercaptobenzothiazole and stead of 2,2'(benzothiazolyl)dithiocarbonate. My prodoxalyl chloride, but the reaction took an entirely different uct, carbonyl bis-3-(Z-benzothiazolinethione), was not course. The reaction was carried out in a one-liter 3- present in the resulting mixture produced when sodiumnecked flask equipped with an aqueous sodium hydroxide 2-mercaptobenzothiazole and carbonyl chloride were retrap in order to remove hydrogen chloride and gas sample acted. However, as I described, supra, when oxalyl chlobottles to collect carbon monoxide and carbonyl sulfide. ride was reacted with Z-mercaptobenzothiazole in an anhy- To a stirred slurry containing 66.9 grams (0.4 mole) of drous medium the new compound, carbonyl bis-3-(2- recrystallized Z-mercaptobenzothiazole in 600 ml. of anhybenzothiazolinethione), was present in the product. drous benzene, 27.9 grams (0.22 mole) of oxalyl chlo- As shown by the data, infra, carbonyl bis-3-(2-benzoride was added dropwise at 50 to 60 C. over a period thiazolinethione) was found to be an active accelerator of 15 minutes. During the addition of oxalyl chloride the for the vulcanization of natural rubber. To illustrate the color of the reaction mixture changed from yellow to accelerating properties of carbonyl bis-3-(2-benzothiabrown and finally to a purple color. The stirred reaction zolinethione), a vulcanizable stock was compounded commixture was heated at reflux for 24 hours. Gas samples prising were taken at one-hour and 5-hour intervals. The in- Parts by Weight frared spectra of these samples were superimposable with Smoked sheets rubber 100.0 authentic samples of carbon monoxide and carbonyl sul- Car on lack 50.0 fide. The stirred reaction mixture was cooled to 30 C. 25 Zinc Oxide 5.0 The solids were removed by filtration and air dried at teari acid 3.0 25 to C. This product, carbonyl bis-3-(2-benzothia- Saturated hydrocarbon softener 3.0 zolinethione), was obtained in 19.4% yield. The carul ur 2.0 bonyl bis-3-(2-benzothiazolinethione) was a yellow crys- Antid gradant 2.0 tal with a melting point of 179180 C. with decomposi- 30 Carbonyl biS-3-(z-befllothialolillefhimle) 0.5 tion. The melting point remained unchanged after recrystallization from dimethylformamide. Analysis gave Vulcamzatlon was completed at a tenfllmramfe 770% nitrogen and 3 5 lf compared to 7 77% and all tests were on 65-minute cures (except the Mooney nitrogen and 35.58% sulfur calculated for C H N O5 scorch). The following results were obtained on the- A molecular weight of 357 was found. The calculated Stock: molecular weight for C H N OS was 360. The infrared Mooney scorch at 135 C i 103 spectrum of carbonyl bis-3-(2-benzothiazolinethione) Modulus of elasticity at 300% elongation (lbs./ was obtained from solutions of chloroform and dimethylin?) 1450 formamide. The spectrum was consistent With the pro- Tensile at break in lbs/in. 2400 posed structure as indicated in Table II, infra. Ultimate elongation (percent) 410 TABLE II 1 'R Assignment s S t O t g i193? lliiitaajjj 82 3 Stfitfiflfif 1,465 medium." C=G skeletal ln-plane group while S-substituted derivatives absorbed in the region of 275 millimicrons with molar absorptivities of approximately 21,000. Therefore, the ultraviolet spectrum was characteristic of carbonyl bis-3-(2-benzothiazolinethione).

In U.S. Patent No. 1,928,773, Williams reported the Another product was isloated from the filtrate of the 2- mercaptobenzothiazole and oxalyl chloride reaction described, supra. The benzene and excess oxalyl chloride were removed in vacuo at a maximum temperature of 30 to 40 C. at 1 to 2 min. pressure. The resulting solids were added to 600 ml. of water containing 64 grams (0.4 mole) of 25% aqueous sodium hydroxide and stirred at 25 to 30 C. for 1 hour. The solids were collected by filtration, washed with water until neutral to litmus and air dried at 25 to 30 C. The product, 2,2'-thiobis(benzothiazole), melting point -97 C. Was obtained in 80.6% yield. After recrystallization from ethyl alcohol, it melted at 101-102 C. Vapor phase chromatographic analysis of samples of the product and recrystallized product gave only one peak. Analysis gave 9.23% nitrogen and 32.03% sulfur compared to 9.33% nitrogen and 32.03% sulfur calculated for C H N S Thus, the dicarbonyl product from Z-mercaptobenzothiazole reacted with oxalyl chloride was not obtained. Instead, a new method for preparing 2,2-thiobis(benzothiazole) was revealed. Further investigation showed that this was a general method for the preparation of 2,2-thiobis(benzothiazoles). For example, the benzene ring of the starting material can be substituted with substituents such as halogen, NO aryl, lower alkyl or lower alkoxy where the alkyl is methyl, ethyl, propyl, isopropyl or amyl. Suitable starting materials comprise 5-chloro-2-mercaptobenzothiazole, 6-nitro-2-mercaptobenzothiazole, 6-methoxy-2-mercaptobenzothiazole, 4-methoxy-2-mercaptobenzothiazole, 6-ethoxy-2-mercaptobenzothiazole, 4-methyl-2-mercaptobenzothiazole and 4- or 6-phenyl-2-mercaptobenzothiazole.

2,2-thiobis(S-chlorobenzothiazole) was prepared in the following manner. To a stirred slurry containing 40.3 grams (0.2 mole) 5-chloro-2-mercaptobenzothiazole in 500 ml. of anhydrous benzene, 14 grams (0.11 mole) of oxalyl chloride was added dropwise at 50 to 60 C. over a 15-minute period. The stirred reaction mixture was heated at reflux for 18 hours. After cooling to 25 C., the solids were collected by filtration. The wet solids were added to 600 ml. of water containing 32 grams (0.2 mole) of 25% aqueous sodium hydroxide and stirred for 1 hour. The solids were collected by filtration, washed with water until the washings were neutral to litmus and air dried at 25 -30 C. The product, melting point 171- 172 C., was obtained in 99% yield. After recrystallization from dimethylformamide, it melted at 172-173 C. The vapor phase chromatographic analysis of the product and a recrystallized sample of the product gave only one peak. Analysis gave 7.40% nitrogen, 26.13% sulfur and 19.38% chlorine as compared to 7.57% nitrogen, 26.05% sulfur and 19.20% chlorine calculated for C H Cl N S The formation of S,S'-bis(Z-benzimidazoyl)-1,2-dithi0- oxalate is significant not only because of the ease with which it undergoes alcoholysis but because of the kaleidoscopic nature of oxalyl chloride. With various reagents, oxalyl chloride reacts like a dehydrating agent, a chlorinating agent or a mixture of phosgene and carbon monoxide as well as like an acid chloride.

It is intended to cover all changes and modifications of the examples of the invention herein chosen for purposes of disclosure which do not constitute departures from the spirit and scope of the invention.

I claim: 1. S,S'-bis(2 heterocyclic)-l,2-dithiooxalates of the formula where Z is selected from the group consisting of O and 10 NH.

2. S,S-bis(2-benzimidazolyl)-1,2-dithiooxalate of the formula 3. S,S-bis(2-benzoxolyl)-1,2-dithiooxalate of the formula References Cited by the Examiner NICHOLAS S. RIZZO, Primary Examiner.

HENRY R. JILES, Examiner.

ALTON D. ROLLINS, Assistant Examiner. 

1. S,S''-BIS(2 - HETEROCYCLIC)-1,2-DITHIOOXALATES OF THE FORMULA 